The invention relates to a method for monitoring a sensor unit arranged in an exhaust region of an internal combustion engine.
The invention further relates to a corresponding device for performing the method.
In order to comply with the statutory limits for emissions from internal combustion engines, various components are used for exhaust gas aftertreatment and sensor units are used to control these systems and to monitor the emissions. Known components for exhaust gas aftertreatment are oxidation catalytic converters, diesel particle filters (DPF), SCR catalytic converters and NOx catalytic converters, for example. Corresponding sensor systems are lambda probes, NOx sensors or particle sensors, for example.
On the basis of statutory provisions currently at the planning stage, for example, the discharge of particulates from an internal combustion engine, in particular a diesel engine, must be monitored upstream and/or downstream of the diesel particle filter (DPF), whilst in operating service. A load prognosis of the diesel particle filter for regeneration monitoring is furthermore required in order to achieve a high system reliability and in order to allow the use of cost-effective filter materials. Provision may furthermore be made for regulating the combustion characteristics of the internal combustion engine on the basis of the information on discharge of particulates.
Under new legislation the monitoring of these components and sensor units for malfunction and unauthorized removal is also to be ensured. This is to be reliably ensured in the context of a so-called on-board diagnosis (OBD).
DE 103 58 195 A1, for example, a method for monitoring a component arranged in an exhaust region of an internal combustion engine, in which a measurement for a first exhaust gas temperature is taken upstream of the component, and in which a second exhaust gas temperature, which occurs downstream of the component, is measured by a second temperature sensor. The intention here is to monitor the low-pass behavior, which is determined by the heat capacity of the component, by evaluating the first exhaust gas temperature in relation to the second exhaust gas temperature and to emit a fault signal in the event of a variation in a predefined measurement for the low-pass behavior of the component.
With this method it is possible to assess the state of the component, which is situated between the two temperature sensors in the direction of flow of the exhaust gas. Thus it is also possible, for example, to detect inadmissible tampering with this component right through to complete removal of the component.
It is not possible to detect, however, whether the sensor unit itself, for example the particle sensor, has been tampered with or even inadmissibly removed.